Electric discharge device



Aug. 23, 1938. w. E. BAHLS ELECTRIC DISCHARGE DEVICE Filed Jan. 10, 19:56

INVENTOR MZZBI'EBd/Z 25.

ATTORN WITNESSES:

working atmosphere.

Patented Aug. 23,

me OFFICE 2,128.0" nwcrnrcnrscnsaoa navron 'Walter E. mm, Wilkinaburg. Pa alaignor to Westinghouse Electric a Manufacturing Company, East "Pittsburgh,

Pennsylvania Pa a corporation of Application January 10, 1938, Serial No. 58,533

3 Claims.

This invention relates to space discharge devices and is particularly adapted to those devices which have a hot cathode and gas or mercury vapor or a combination of the two for their It is a further object 01 the invention to provide a circuit such that the single grid controlling the device having a cathode and a plurality of anodes may have impressed upon it a controlling potential.

It is a further object of this invention to provide a circuit of the sort described in which the part of the cycle during which any one anode carries current may be a predetermined fraction of a cycle. 1

It is a further object of this invention to provide a shield which shall act as a barrier separating the anodes.

It is a further object of this invention to so locate the openings in said barrier that they shall, in effect, provide substantially distinct paths between the cathode and the several anodes, and any particular path shall be free and unobstructed between the cathode and its anode.

It is a further object of the invention to so select the atmosphere in the tube, gas, mercury vapor, or mixture of gas and vapor, that the arc drop and the starting potential shall have the 'desired values.

Other objects of the invention and details of the proposed structure will be apparent from the following description and the accompanying drawing, in which Figure 1 is a central vertical sectional view of one form of my device. a

Fig. 2 is a similar view, the plane of the section being at right angles to that of Fig. 1.

Fig. 3 is a similar section of another form of my device.

Fig. 4 is a sectional view taken on the line IVIV of Fig. 3..

Fig. 5 is a sectional view taken on the line V-V 01' Fig. 4, and

this invention to produce a several portions united together.

Fig. 6 is a circuit diagram illustrating one use I a cathode 3. The cathode is provided with a heating circuit including leads I and 6 which extend through the press 2 to the ends of the cathode proper 3. The cathode proper consists of a corrugated ribbon wound into helical form and secured to the two leads 5 and 6. From one of the leads depends a support I holding a supply 8 of a getter-metal'which acts as a clean-up device when freeing the tube from gas prior to filling it with the desired atmosphere.

The tube has two anodes l and H supported from the press by leads l2 and [3. Where the lead I2 emerges from the press, it is surrounded by an insulator M which may be the same glass as the press or may be other ceramic material. Similarly, the lead I3 is surrounded with insulator IS. The insulators i4 and I surround the leads substantially up to the terminal blocks II and II which constitute the anodes proper.

A hollow cylinder l8 surrounds the anode HI and a cylinder l9 surrounds the anode II. The

cylinders may be made of sheet metal and pro-.

vided with flanges 2| and 22 by which the two halves of the cylinders are joined together. A similar flange 23 constitutes the middle portion of the shield and the junction of the two cylinders. The shield as a whole namely l8, l9, 2|, 22 and 23 is designated 24 and it may be supported from the press by a standard 25. It is electrically continuous although it may have been made of As shown in the illustration, the flanges 2|, 22 and 23 are spot welded together but any other desirable way of uniting them into an electrically continuous whole may be employed. It is unnecessary to resort to connections outside the tube to make the whole shield electrically continuous but all parts of the shield are connected within the envelope and if desired the connection of the shield to the cathode is also within the envelope.

The inside of the envelope is equipped as shown at 26 with a conductive coating preferably formed by covering the inside or the envelope with a graphite solution. A conductor 28, preferably of very fine flexible wire, extends upward from one terminal of the cathode 3 into contact with the coating 26. The whole of the inside of the envelope is not coated, but only the portion adjacent one end of the space discharge paths. In the form shown in Figs. 1 and 2 the coating extends slightly below the upper end of coating extends slightly belowthe anodes.

The thin and flexible wire 23 is at one end of the cathode, and the cathode, anodes and shield are mounted in the press before-the press is united with the rest of theenvelope. When the tube is completed by putting the press into its place within the rest of .the envelope, the wire 23 comes into contact with the coating 2'; No special care need he exercised in determining the length of the wire 23, as it is made long enough to surely contact the envelope and can bend to accommodate itself to the space in which it is finally located. r It will be'seen upon inspection of the shield shown in Fig. 1 that there is a direct line from the anode l0 to the left hand part of the cath-, ode 3 uninterrupted by the shield and similarly .a. direct line from anode II to the right-hand part of the cathode 3 is not crossed by the shield. By a direct line I do not necessarily mean a straight line, but one over which ions can travel without change of direction abrupt enough to materially increase the likelihood of the ions going somewhere else instead of to the cathode,

In Fig. 3 the anodes ill and H are at the upper ends of standards continuous with the leads I! and I3. The cathode is heated through leads ,I and 0 which extend to. its twoends, as shown most clearly in Fig. 5. A trough-shaped portion of the shield surrounds the cathode except at the top thereof and is equipped with insulators 3| and 32 through which the leads 5 and 6 extend. The trough "is open at the top and the opening is divided by a shield 33 which extends between the anodes it and it into the space surrounded by the coating 26. 7

The shield 33 is supported bytwo portions 35 and 36 which extend downwardly along the end walls of the trough. The central portion of the shield 33 extends into the interior of the trough, abutting the inner face of the end portions as shown at 3'8 and 38. The lower edge 38 of the shield is as near to the cathode 3 as it can conveniently be located without danger of contact therewith. The trough 30 is supported by a pair of standards 4! and 42 which are joined together and supported from the press as clearly shown in Fig. 3 at W. A weld or other securing means illustrated at 48 unites each standard to the trough.

It will be noted that the shield of Fig. 3 afi'ords a direct line from the left hand part of cathode 3 through the left hand half of the top of the trough to anode i0 and a direct line from the right hand part of the cathode through the right hand half of said top to anode Ii.

In Fig. 6 the cathode leads 5 and 6 and the anodes I0 and II are identified by the same numbers. The shield designated 50 in Fig. 6

may have either the form'shown in Fig. 1 or that shown in Fig. 3, or any other desired form. The

standards supporting the shield are illustrated in Figs. 1 and 3 as if they terminated in the press.

The coating 26 in Fig. 3 is connected by a fine flexible wire 23 to the shield. The coating is thus kept at the same potential as the shield.

JIhis is different from the arrangement of Fig. 1

in which when the shield connections are inside of the envelope the coating is connected to the other end of the cathode from the shield. If it is desired to control the potential of the shield by connections outside of the envelope, the standard must extend through the envelope as indi- 8,198,070 the shield 34. In thefform shown in?! 3'the cated in Fig. 6 by the lead II. For supplying power to the anodes a transformer "is shown in Fig. 6. A small secondary of the same transformer or of another, not'shown, is indicated at I53, as supplying the leads I and I and the oathode.

Each anode is connected to the respective end of the secondary of transformer 53. 4 The center of said secondary is connected to the center of the secondary 53 and thus to the cathode. The connection includes the load which is represented by the resistor 54 although it ,need not be merely resistive.

The primary 5! of a transformer I is illustrated as connected in parallel with the primary of transformer 52. The transformer 3! includes a primary 55, a coil 51 and a secondary coil II.

The coil 51 is connected to the'same terminals as the coil 55, an adjustable resistor 53 being included in one connection. The electromot ive forces induced in the secondary 53 are dependent both as regards phase and intensity on the ad- Justment of the resistor 53. The coil 53 delivers current to a full wave rectifier 83, preferably of the copper oxide type, whereby current flows through one-half of the coil 33 and one-half of the full-wave rectifier during one-half cycle, and through the other half of the coil and the other half of the rectifier during the next half cycle. The transformer is so designed that the current delivered by the secondary 53 has a sudden rise to a maximum each half-cycle with small current during the other portion of the half cycle. Although the drawing indicates one way of designing such a transformer, other ways may be used.

The return connection from the rectifier to the middle of the coil 58 is through a resistor 30. A connection between the end of the resistor 80 nearest the rectifier and the shield 50 is made by means of a resistor 6|. A battery 82 is connected between the end of the resistor 60 nearest the transformer 55 and the middle of the secondary 53.

When the tube is completed and evacuated it is filled with neon or other desired gas to the pressure decided upon. A small amount of mercury is also introduced if desired. With low pressure gas only the voltage drop along the arcs formed between cathode and the several anodes is greater than if mercury also is present. With -mercury present the current characteristics of connection between the shield and a point of predetermined potential, such as one end of the cathode, may be made within the tube. The standard 25 does not then extend outside ofthe press. When this connection is used, the flexible connector 28 is connected to the opposite end of the cathode 3 so that the shield is -at the potential of one end of the cathode 3 and the interior coating is at the potential of the opposite end.

When the tube is thus connected, during the half cycle when the anode I 0 is positive, electrons flow from the cathode 3 to the anode II. In the are thus established, there is a drop in potential close to the cathode v3 the gradient of which is much greater than the gradient throughout the rest of the arc. In this space where the gradient is large, the electrons from the cathode travel at a speed sumcient to produce more ionization than elsewhere in the gas with which the is small.

cathode space-charge sheath.

The sheath in which the electrons produce most ionization in. the gas has a well-marked boundary. 'Its thickness varies with the pressure and the current density. As the current density becomes greater this region becomes more narrow. Within this region the ions which are formed by the ionization are subjected to strong attraction from the cathode. Most of these ions fall into the cathode but not with sufllcient velocity to damage it because the distance they fall Electrons which escape from the space charge sheath move to the anode Hi. There will not be much acceleration of these electrons be tween the boundary of the space-charge sheath and the anode because the potential gradient here is small. It is small because the space charge to be overcome is small, being largely neutralized by the ions present. The ions here are acted upon by a-potential gradient small compared to that within the space-charge sheath. The erratio motion of the ions, similar to that of gas molecules, therefore, produces a more readily recognized effect here than in the space-charge sheath. That is the ions in the long part of the arc diffuse more than those in the narrow space-charge sheath. The ions within the sheath do not diifuse much because of the stronger electrostatic forces there. The diffusion of ions tends to produce ionization throughout the tube but into the cylinder I3 surrounding the negative.

anode ll, very few ions will enter.

Ions between the mouth of cylinder l9 and the cathode are attracted by the cathode 3, which has a negative potential. The anode II has a much stronger negative potential but it is sur; rounded by the cylinder I! which is at the potential of one end of the cathode. The space between the cathode 3 and the adjacent mouth of the cylinder I 9 is near the coating 26 which differs from the potential of the shield I9 by only a small amount. s i

The attraction of the negative anode ll upon the ion between the cathode 3 and the opening at the upper end of the cylinder l9 is'largely neutralized by the shield 24 and the coating 26. They therefore move toward the cathode 3.

It is different with the ions between the oathode 3 and the mouth of the cylinder It. The anode Ill therein is strongly positive at the time and an arc is maintained between it and the cathode 3, the ions in said are moving toward the cathode and the electrons therein moving toward the anode in the usual way. Therefore, although the ions in the long part of the arc stream can diffuse and do diffuse, very few of them enter the region enclosed by the cylinder around the tween the anodes be high, it is necessary that the edges of the cylinders l8 and I 9 be fairly. close to the cathode 3. In general it may be said that the distance from the cathode to the nearest edge of the opening in the shield ought not to be more than ten times the thicknessof the abovedescribed space-charge sheath. 0n the other but within which little diffusion occurs.

hand, the shield can act as a grid, preventingthe are from starting to the positive anode until a certain critical potential has been passed. The nearer the edge of the opening 'in the shield to the cathode, the greater is this grid effect. It is, therefore, undesirable to have the shield much closer to the cathode than the above-specified distance of ten times the thickness of the spacecharge sheath.

The device can be used effectively with high anode potentials because back-fire does not occur for even at high potential a discharge will. not form between the anodes. Around the negative anode the shield and coating present a region where the field is insufiicient compared to the field of the cathode to move ions to the negative anode in sufilcient number to form an arc. The negative anode is thus protected from anarc thereto being established. I

In the modification shown in Figs. 3 to 5, similar considerations apply. The anodes are not surrounded by the shield in this form, but a barrier is presented by the shield 33 which, together with the trough 30, affords an electrostatic shield at a potential corresponding to one end of the cathode.

side the envelope as illustrated in Fig. 6, or by other external connections if desired. This barrier prevents ions from being attracted by the negative anode. Although the negative potential of the negative anode is strong compared to the negative potential of the cathode, the ions do not proceed to the negative anode because of this electrostatic action of the shield. Around the cathode .is formed the above-described spacecharge sheath, outside of which ions-may diffuse, Ions may proceed by diffusion to fill the space on one side of the partition 33 within the trough and form an arc stream between the trough and the positive anode, but few ions will be present in the tube on the side of the partition 33 toward the negative anode.

When it is desired that the shield shallact as a grid in either form of the device, it may be connected to an external source of potential, as indicated in Fig. 6. At the beginning of any particular cycle, current will flow through the resistor- Bll and through one-half, of the rectifier 63. This current is toward the left in Fig. '6. The right hand end. of the resistor 60 is therefore more positive than the lower end of the battery 82 and the drop over the resistor must be subtracted from the potential provided by the battery to obtain the potential of shield 50. When the resultant potential of the shield is no longer sufficiently negative to prevent the formation of an arc, the arc starts. By proper adjustment of the resistor 59, and, if necessary, adjustment of the ratio between the potential of the battery 62 and the resistance of the resistor 60, this critical potential of the shield may be reached at any desired period in the half cycle. All of these adjustments except that of the resistor 59 are preferably permanent and made when the apparatus is first designed or manufactured. The anode, which is at this time active, can be made, therefore, to carry current during only a fraction of that half cycle, and thus the average current carried-by that anode can be regulated.

During the next half cycle, the current flows through the other half of the rectifier 63, but is in'the same direction through the resistor ill, and,

If preferred the. potential of the shield may be controlled by connections extending outthe shield therefore, arrives at, the critical poten- 75 tial at the same fraction of the next hall cycle. The other anode will thus carry an adjusted por tion of current in the same way.

Another way of regulating the starting voltage is by proper choice ofthe atmosphere filling the tube. II the atmosphere be wholly a gas, such as neon, the starting potential is smaller, but the voltage drop across the arc is higher than it the tube be filled with mercury vapor. By proper combination of the two, any desired relation between the starting voltage and the arc drop can be obtained.

If the tube has some liquid mercury in it when cold, the heat generated within the tube when energized will vaporize the mercury increasing the mercury vapor in the tube. The mercury vapor will cause a diminution in the arc drop and thus, at constant output, a diminution in the heat produced. The tube will soon arrive at a steady state in which the temperature is constant andthus the pressure in the tube is also constant. Thus the voltage drop and the starting potential will each be fixed.

In order to disclose this invention more completely, I am stating here the dimensional details concerning one type of this tube which is in extensive commercial use. I do not wish to be understood as saying that this is the only type which has achieved commercial success, nor do I intend the specification and claims to be limited by the dimensional description here given. This tube is used as a full-wave rectifier. The cathode is oxide coated and directly heated. The heating current is 6.4 amperes and is supplied with 2.5 volts. It requires 30 seconds to reach its working temperature when starting cold. The" alternating voltage between the anodes may be as high as 440 volts, and the average anode current output may be as high as 1 ampere. When an anode reaches a potential of 30 volts positive with respect to the cathode, it will always have started to carry current and the arc drop for the conductive period will average about 13 volts. The tube is 6% inches long from the top of the part of the envelope, which is coated interiorly at 26 to the bottom of the connecting pins upon the socket, which is not shown in the drawing. It is 2%; inches in diameter. It is filled with argon to a pressure of 0.6 millimeter of mercury and is air cooled. The filament consists of seven turns- 01- corrugated ribbon, .075 inch wide, and .007 inch I thick. It is 5% inches long before being corrugated and 4% inches long after corrugating. It

' is wound into a coil of seven turns, 1 of an inch between ends, inch being allowed at each end for mounting. The shield 24 has a cylinder .531 inch internal diameter. The two external flanges are of an inch wide. The flat part of the central flange is 5'0! an inch wide, and the central part has .062 inch internal diameter where it fits the standard 2!.

It will be apparent to those skilled in the art that many modifications besides those here expressly described, can be produced. I, therefore,

do not desire that the invention be limited to what is here explicitly described. No limitation not required by the prior art or expressed by the claims is intended.

I claim as my invention:

1. A space discharge device including an envelope, a cathode and a plurality of anodes, an electrostatic shield electrically continuous within the envelope separating said anodes and forming a chamber about each anode with an opening for each anode which leaves the direct line from such anode to the cathode unimpeded, said shield extending across all direct paths between any two anodes.

2. A space discharge device including an envelope, a cathode and a plurality of anodes, a plurality of metal cylinders, open ends on said cylinders, said anodes being respectively positioned within said cylinders, said cylinders constituting electrostatic shields electrically continuous within the envelope and crossing all direct paths between any two anodes while said open ends leave unimpeded the direct line from each anode to said cathode.

3. A space discharge device comprising a cathode comprising a solid conducting body, a pair of anodes, and a pair of interconnected metallic cylinders within which said anodes are respectively positioned to form a single electrically continuous electrostatic shield having a portion interposed between said anodes, said shield having two openings through which the direct lines from each anode to the cathode pass.

WALTER E. BAHLS. 

